labVIEW time domain-frequency domain analysis

   Frequency domain (frequency domain) - the independent variable is frequency, that is, the horizontal axis is frequency and the vertical axis is the amplitude of the frequency signal , which is usually called a spectrum diagram . The spectrum diagram describes the frequency structure of the signal and the relationship between the frequency and the amplitude of the frequency signal.

　　When performing time domain analysis on signals, sometimes the time domain parameters of some signals are the same, but this does not mean that the signals are exactly the same. This is because signals not only change with time, but also depend on frequency, phase and other information. This requires further analysis of the frequency structure of the signal and description of the signal in the frequency domain.

 

    

   Next, let's take a simple example in labVIEW to explain:

    The front panel is shown in the figure:

      Rear Panel:

 
    This example uses a sine signal generator to generate a sine signal. The waveform diagram displays the time domain signal in real time. After Fourier transform, the frequency structure of the signal is displayed in the frequency domain.

     The Sine Signal Generator VI is:

Its meaning is as follows:

     As we can see above, the output value of the time domain signal after FFT conversion in the program is the sum of the signal amplitudes, so we need to find the mean value and then separate the complex number into the amplitude. The "Complex to Polar Coordinates Conversion VI" is used, and its specific functions are as follows: 

Signal analysis:

   1. The amplitude after Fourier transformation is halved;

   2. The amplitude corresponding to the frequency of 0 is the amplitude of the DC component in the signal;
   3. The low frequency contains the waveform frequency, and the high frequency is the difference between the sampling frequency and the waveform frequency. (To be studied)